Circuit arrangement for operating a multi-phase synchronous motor in a direct voltage network

ABSTRACT

A circuit arrangement for operating a multi-phase synchronous motor includes a switching device (13) composed of semiconductor switches (14-16) for the successive connection of the winding phases (u, v, w) of the armature winding (10) to a direct mains voltage and a commutation device (21) for the actuation of the semiconductor switches (14-16) in the correct sequence by means of switching signals (S1-S3) in conformance with the rotary position of the rotor. In order to reduce commutation noise and radio interference with low circuit engineering expenditures, each control input (G) of the semiconductor switches (14-16) is preceded by an analog difference former ( 18-20 ) which receives, on the one hand, the switching signal (S1-S3) associated with the semiconductor switch (14-16) and, on the other hand, a reference signal derived from the phase sum current of the armature winding (10). The semiconductor switches (14-16) are here fully energized as long as the amplitude of the switching signal (S1-S3) is greater than the amplitude of the reference signal.

BACKGROUND OF THE INVENTION

The invention is based on a circuit arrangement for operating asynchronous motor of the type defined in the preamble of claim 1 andincluding a multi-phase armature winding in a direct voltage network.

In a known circuit arrangement of this type for a three-phasesynchronous motor (DE 3,940,569) the switching signals are configured,in order to reduce commutation noise and radio interference, so that thetwo switching signals for the semiconductor switches associated with thecommutating winding phases overlap one another in time. In the overlapregion, one of the two switching signals is clocked in such a way thatthe average of the phase current increases in the up-commutating windingphase and decreases in the down-commutating winding phase, namelylinearly or according to an exponential function. However, this type ofcommutation requires relatively high expenditures for circuitry.

SUMMARY OF THE INVENTION

In contrast thereto, the circuit arrangement according to the inventionincluding the characterizing features of claim 1 has the advantage oflow expenditures for circuitry with relatively little commutation noiseand very low radio interference which makes additional interferencesuppression measures unnecessary. During the commutation, that is,during the transition of the current from the one winding phase to theother winding phase, the analog control of the semiconductor switcheshas a positive effect in that only a slight current steepness occurs.This again causes only slight excess voltages so that inverse diodes andvoltage limiters are not required. Because of the absence of the steepswitching edges, there is also hardly any radio interference and thecommutation noise is noticeably reduced.

The measures defined in the further claims permit advantageousmodifications and improvements of the circuit arrangement defined inclaim 1.

According to a preferred embodiment of the invention, the referencesignal is picked up as a voltage drop across a resistor through whichflows the phase sum current of the armature winding and is suitablyamplified.

The circuit arrangement according to the invention can be employed forsynchronous motors in which the winding phases of the armature windingare connected in a wye configuration, independently of whether theneutral point is brought out or not.

If the neutral point is brought out, a so-called half-wave control canbe realized if, according to one embodiment of the invention, asemiconductor switch is connected in series with a respective windingphase and the parallel series connections are connected with the directmains voltage, on the one hand, by way of the neutral point and, on theother hand, by way of the resistor which picks up the winding sumcurrent.

A so-called full-wave control can be realized if, according to a furtherembodiment of the invention, pairs of semiconductor switches areconnected in series and a winding phase of the armature winding isconnected at each one of their respective connection points. Thisresults in a number of parallel series connections which correspond tothe number of winding phases or conductors. The parallel seriesconnections are connected jointly to the direct mains voltage by way ofthe resistor for picking up the sum current in the armature winding.This full-wave control improves motor utilization. The number of phasesin the armature winding is not subject to any limitations. If athree-phase winding is involved, the armature winding may also beconnected in a delta configuration.

In a preferred embodiment of the invention, an operational amplifier,more precisely a differential amplifier, is employed as the differenceformer and a power MOS field effect transistor (power MOSFET) isemployed as the semiconductor switch. This results in a low-powertransistor actuation.

According to a further embodiment of the invention, the edges of theperiodic rectangular pulses of which the switching signals are composedare sloped at an angle less than 90° so that the ascending edges of therectangular pulses of the switching signal associated with the nextarmature winding phase in the direction of current flow and thedescending edges of the rectangular pulses of the switching signalassociated with the preceding winding phase in the direction of currentflow overlap one another in time. With this configuration of theswitching signals, the commutation noise can be reduced even morenoticeably.

According to a further embodiment of the invention, the amplitudes ofthe switching signals are limited as a function of the number ofrevolutions, which can be realized by means of a revolution controllerconfigured as a P or PI controller. The actual number of revolutions ishere derived from the switching signals.

BRIEF DESCRIPTION OF THE DRAWING

In the description that follows, the invention will be discussed ingreater detail with reference to embodiments thereof that areillustrated in the drawing, in which:

FIG. 1 is a circuit diagram of a circuit arrangement for operating athree-phase synchronous motor with electronic commutation (EC motor) ina direct voltage network;

FIG. 2 is a block circuit diagram for the difference former andsemiconductor switch in the circuit arrangement of FIG. 1;

FIG. 3 is a diagram of various signals in the circuit arrangementaccording to FIG. 1;

FIG. 4 is a block circuit diagram for a circuit arrangement foroperating a three-phase EC motor according to a further embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the block circuit diagram shown in FIG. 1, the reference numeral 10identifies the three-phase armature winding of the synchronous motorwhose winding conductors or winding phases u, v, w are accommodated inthe stator of the synchronous motor. The rotor, which is configured as apermanent magnet rotor, is marked 11. It is here shown symbolically ashaving two poles, but may also have a different number of poles. Thewinding phases u, v, and w are combined at their one winding end into aneutral point 39 which is brought out of the synchronous motor and isconnected to the positive pole "+" of a direct voltage network 12. Thethree free winding terminals 36, 37 and 38 of the three winding phasesu, v, and w that are disposed on a terminal board are connected with aswitching device 13 which is connected to the other potential of thedirect voltage network.

Switching device 13 includes three schematically shown power transistors14, 15, and 16 which are each connected in series with one of thewinding phases u, v, and w. As can be seen in conjunction with FIG. 2,each power transistor 14-16 is formed by a power MOSFET 22 whose drain Dis connected to the associated winding phase u or v or w, respectively,and whose source S is connected by way of a resistor 17 to the lowerpotential of the direct voltage network 12. The sources S of all powerMOSFET's 22 are here connected to the direct voltage network 12 by wayof the same resistor 17. Power transistors 14, 15 and 16 are controlledby difference formers 18, 19 and 20 which receive, on the one hand, thereference signal derived from the sum current of armature winding 10and, on the other hand, switching signals generated by a commutationdevice 21 as a function of the rotary position of the rotor. Accordingto FIG. 2, each difference former 18-20 is formed of a differentialamplifier 23 whose output is connected with the gate G of power MOSFET22. The reference signal is here applied to the inverting input 231 andthe switching signal to the non-inverting input 232 of differentialamplifier 23. In order to obtain the reference signal, the voltage dropacross resistor 17 is picked up, is converted by means of an amplifier24 into a sufficiently high voltage and is then applied to the invertinginputs 231 of the three differential amplifiers 23.

The switching signals generated in commutation device 21 are shown inFIG. 3 and are there--as in FIG. 1--marked S1, S2 and S3. In each case,one of the three switching signals S1-S3 is connected to thenon-inverting input 231 of the difference formers 18-20 which are eachconfigured as a differential amplifier 23. To generate the switchingsignals, three stationary position sensors 25, 26 and 27 that are offsetrelative to one another by the same circumference angles are arranged atthe rotor circumference and generate output signals H1, H2 and H3corresponding to the rotary position of rotor 11. These output signalsfrom position sensors 25-27 are shown at the top of FIG. 3. In a gatingcircuit 28, these three output signals H1, H2 and H3 are converted intoa three-phase signal A1, A2, A3 without overlap and with a pitch of2π/3. The three-phase signal A1, A2, A3 is fed to a block 29 whichlimits the steepness of the rectangular pulses. The three switchingsignals S1', S2' and S3' are present at the output of block 29, eachcomposed of a sequence of periodic rectangular pulses whose ascendingand descending edges extend at an angle of less than 90°. Since thethree switching signals S1', S2' and S3' are mutually shifted in phaseby 2π/3, the same as the three-phase signal A1, A2, A3, the ascendingedges of the rectangular pulses of the switching signal associated withthe subsequent winding phase of armature winding 10 in the direction ofcurrent flow and the descending edges of the rectangular pulses of theswitching signal associated with the preceding winding phase of armaturewinding 10 in the direction of current flow overlap one another in time.These switching signals S1', S2' and S3' which essentially correspond tothe switching signals S1-S3 at the output of commutation circuit 21shown at the bottom of the diagram, could now be fed directly to thenon-inverting inputs 232 of the three differential amplifiers 23. In thecommutation device 21 employed here, switching signals S1'-S3' areadditionally limited as a function of the number of revolutions. Forthis purpose, switching signals S1', S2' and S3' are fed to threedifference formers 31, 32 and 33 which subtract a value put out by arevolution controller 30 from the amplitudes of switching signals S1',S2' and S3', so that now switching signals S1, S2 and S3 are present atthe output of commutation device 21, which are each fed to one of thethree difference formers 18-20. Revolution controller 30 is configuredas a P or PI controller which receives the difference between apredetermined set revolution value n_(set) and a measured actualrevolution value n_(act). For this purpose, revolution controller 30 ispreceded by a further difference former 34 to which is applied, on theone hand, the set revolution value n_(set) and, on the other hand, theactual revolution value n_(act). The actual revolution value n_(act) isdetermined in a block 35 by an evaluation of the edges of signals A1-A3.

In the circuit arrangement shown in FIG. 4, the neutral point 39 of thethree-phase armature winding 10 connected in wye configuration is notaccessible, only the three winding terminals 36, 37 and 38 which aredisposed on a terminal board. Here, switching device 13' as a wholeincludes six power transistors 41-46 all configured as power MOSFET's 22according to FIG. 2. Pairs of power transistors are here connected inseries, for example 41 and 44, 42 and 45, and 43 and 46. Their commonconnection point is connected in each case with one of the windingterminals 36-38. All three series connections of power transistors 41-46are connected in parallel and the parallel connection is connected byway of resistor 17 to the direct voltage network 12. The drain D is hereconnected with the positive pole "+" of direct voltage network 12 andthe source S with resistor 17 which is connected with the negative poleof direct voltage network 12. Each gate G is again preceded by adifference former 51-56 which, as in FIG. 2, is configured as adifferential amplifier 23. In the same manner as in FIGS. 1 and 2, thevoltage drop picked up across resistor 17 and suitably amplified byamplifier 24 is fed to the inverting inputs 231 of difference formers51-56 and switching signals S1-S6 from commutation device 21' are fed tothe non-inverting inputs 232. In this circuit arrangement, a so-calledfull-wave control of the EC motor is realized in contrast to thehalf-wave control performed in the circuit arrangement of FIG. 1. Thisfull-wave control results in a better utilization of the EC motor. In athree-phase armature winding 10, the winding conductors or windingphases u, v, and w may also be connected in a delta configuration. Thecommutation device 21' furnishes a total of six switching signals S1-S6which are derived from the output signals H1-H3 of position sensors25-27, with switching signals S1-S6 being shifted in time relative toone another in a suitable manner so that two of the power transistors41-46 are conductive simultaneously to perform the full-wave control andthese two power transistors 41-46 are conmutated successively each timein conjunction with a further power transistor.

The invention is not limited to the above-described embodiments. Inparticular, the number of phases of the armature winding is subject tono limitations.

Instead of obtaining the switching signals from the position sensors,the switching signals may also be obtained by sensor-less detection ofthe position of the rotor, utilizing the voltage induced in the armaturewinding. Such a sensor-less position detection is disclosed, forexample, in DE 3,042,819.A1.

I claim:
 1. A circuit arrangement for operating a synchronous motorincluding a multi-phase armature winding in a direct voltage network,the arrangement comprising a switching device for the successiveconnection of the winding phases of the armature winding to a directmains voltage, the switching device including a plurality ofsemiconductor switches that are associated with the individual windingphases, and a commutation device for the actuation in the propersequence of the semiconductor switches by means of switching signals inconformance with the rotary position of the rotor of the synchronousmotor, characterized in that each control input (G) of the semiconductorswitches (14-16; 41-44) is preceded by an analog difference former(18-20; 51-56) which receives, on the one hand, the switching signal(S1-S3; S1-S6) associated with the semiconductor switch (14-16; 41-46)and, on the other hand, a reference signal derived from the phase sumcurrent of the armature winding (10); and the actuation of thesemiconductor switches (14-16; 41-46) is effected by the differenceformers (18-20; 51-56) in such a manner that the semiconductor switches(14-16; 41-46) are fully energized as long as the amplitude of theswitching signal (S1-S3; S1-S6) is greater than the amplitude of thereference signal.
 2. A circuit arrangement according to claim 1,characterized in that the reference signal is formed by suitableamplification from the voltage drop picked up at a resistor (17) throughwhich flows the phase sum current of the armature winding (10).
 3. Acircuit arrangement according to claim 2 in which the neutral point ofthe armature winding that is connected in a wye configuration is broughtout, characterized in that each semiconductor switch (14-16) isconnected in series with a respective winding phase (u, v, w) of thearmature winding (10) and the series connections are connected inparallel with the direct mains voltage via the neutral point (39) andthe resistor (17).
 4. A circuit arrangement according to claim 2 for ain which the armature winding is connected in a wye configuration,characterized in that pairs of semiconductor switches (41, 44 and 42, 45and 43, 46, respectively) are connected in series and a winding phase(u, v, w) of the armature winding (10) is connected to the respectiveconnection point (36-38) of the semiconductor switches; and the numberof parallel series connections of pairs of semiconductor switches(41-46) corresponding to the number of winding phases (u, v, w) areconnected by way of the resistor (17) to the direct mains voltage.
 5. Acircuit arrangement according to claim 1, characterized in that adifferential amplifier (23) is employed as the difference former (18-20;51-56) and a power MOSFET (22) is employed as the semiconductor switch(14-16; 41-44); and the reference signal is applied to the invertinginput (231) of the differential amplifier (23) while the associatedswitching signal (S1-S3; S1-S6) is applied to the non-inverting input(232) of the differential amplifier (23).
 6. A circuit arrangementaccording to claim 1, characterized in that each switching signal(S1-S3) is composed of periodic rectangular pulses whose edges ascendand descend at an angle less than 90°; and the ascending edges of therectangular pulses of the switching signal (S1-S3) associated with thenext winding phase (u, v, w) of the armature winding (10) in thedirection of current flow and the descending edges of the rectangularpulses of the switching signal (S1-S3) associated with the precedingwinding phase (u, v, w) in the direction of current flow overlap oneanother in time.
 7. A circuit arrangement according to claim 1,characterized in that the amplitudes of the switching signals (S1-S3)are limited as a function of the number of revolutions.
 8. A circuitarrangement according to claim 7, characterized in that the limitationof the number of revolutions is effected in the difference formers(31-33) which each receives, on the one hand, a switching signal(S1'-S3') and, on the other hand, the output signal of a revolutioncontroller (30).
 9. A circuit arrangement according to claim 8,characterized in that the revolution controller (30) is a P controlleror a PI controller which receives the difference between the actualnumber of revolutions (n_(act)) measured at the rotor (11) and a setnumber of revolutions (n_(set)).
 10. A circuit arrangement according toclaim 9, characterized in that the actual number of revolutions(n_(act)) is derived from the switching signals (A1-A3).